The present invention relates to a flexible pipe for transporting, over long distances, a fluid that is under pressure and possibly at a high temperature, such as a gas, petroleum, water or other fluids. The invention relates most particularly to a pipe intended for offshore oil production. It relates especially, first, to the bottom pipes, called “flow lines”, that is to say flexible pipes unwound from a barge in order to be laid generally on the bottom of the sea and connected to the subsea installations, such pipes working mainly in static mode, and, second, to the rising columns, called “risers”, that is to say flexible pipes connecting a surface installation such as a platform to the installations on the seabed and most of which do not lie on the seabed, such pipes working essentially in dynamic mode.
The flexible pipes used offshore must be able to withstand high internal pressures and/or external pressures and also withstand longitudinal bending, twisting or pulling without the risk of being ruptured.
They have various configurations depending on their precise use but in general they satisfy the constructional criteria defined in particular in the standards API 17 B and API 17 J drawn up by the American Petroleum Institute under the title “Recommended Practice for Flexible Pipe” and “Specification for Unbonded Flexible Pipe”. Reference may also be made to documents FR 2 654 795 A, WO 98/25 063 A, FR 2 727 738 A, and FR 2 744 511 A.
A flexible pipe comprises in general, from the inside outward:                a structural assembly able to resist radial forces, composed of a sealing sheath made of a plastic, generally a polymer, able to resist to a greater or lesser extent the chemical action of the fluid to be transported, and of a winding of a metal element wound in a helix with a short pitch;        at least one ply (and generally at least two crossed plies) of tensile armor tendons wound with a long pitch, that is to say one whose lay angle measured along the longitudinal axis of the pipe is less than 60°; and        an external protective sealing sheath made of a polymer.        
In pipes called “smooth-bore” pipes, said structural assembly consists of:                said internal sealing sheath; and        a pressure vault resistant mainly to the pressure developed by the fluid in the sealing sheath and to the external pressure and consisting of the winding of one or more interlocked profiled metal wires (which may or may not be self-interlockable) wound in a helix with a short pitch (that is to say with a winding angle of close to 90°); the profiled wires have a cross section in the form of a Z or a T or derivatives thereof (teta or zeta) or in the form of a U, or more advantageously in the form of an I (cf. document WO 00/09 899).        
In a “rough-bore” pipe, there is furthermore provided, inside the internal sealing sheath, a carcass consisting of an interlocked metal strip that serves to prevent the pipe from collapsing under the external pressure being exerted on said sheath. A pressure vault may be used, too, in order also to contribute to the collapse resistance.
Hitherto, tensile armor tendons have been produced from drawn profiled wires which, for production reasons, are limited to width-to-height ratios (L/H) of less than 4, which means there is a large number (around 40) of wires in each armor ply. These wires are obtained from steel produced in a steelmaking plant by three factory conversion steps, firstly in the form of blooms, then, after rolling, in the form of coils of untreated wire, and then, after a possible heat treatment and drawing and/or rolling, in the form of coils of finished wire. Non-interlocked wires of rectangular cross section are often used for the armor tendons, but it has already been proposed, in document FR 2 664 019, to use, for the first ply of armor tendons, interlockable wires, either by themselves (self-interlockable wires) or together with a secondary interlocking wire. In document FR 2 182 372, it is recommended to produce armor plies interlocked with a Z-shaped profiled wire. Profiled wires have good mechanical properties (mechanical strength Rm of around 800 to 1400 MPa) but are relatively expensive, especially when the wire is relatively wide and/or of complex shape. In addition, it becomes more difficult to use them when they are wide and thick, or when they have a relief; a prior forming operation is then generally necessary, which increases the manufacturing cost.